1. Field of the Invention
The present invention relates generally to a head carriage assembly drive system and disk drive, and more particularly, to a head carriage assembly drive system and disk drive suitable for high-density recording.
2. Description of the Related Art
At present, high-density recording is being introduced to 3.5-inch and other types of magnetic disk drives. In order to increase the recording density, however, it is necessary to increase the number of tracks per unit length of magnetic disk, or TPI, and increasing TPI decreases the width of each track and requires a consequent enhancement in the accuracy with which the magnetic head is positioned. Increasing the TPI to 25,000, for example, reduces the track pitch to 1 xcexcm, requiring the positional accuracy of the magnetic head to be within 0.1 xcexcm. Additionally, such magnetic head positional accuracy should be accomplished with a reduced consumption of power because the magnetic disk drive is operated by a battery mounted in a laptop-type computer.
Conventionally, however, it is difficult to accomplish such accuracy with reduced power consumption due to the configuration of the conventional head carriage assembly drive system.
Accordingly, it is an object of the present invention to provide a head carriage assembly drive system and disk drive in which the problem of obtaining a reduction in energy consumption as described above is solved.
The above-described object of the present invention is achieved by providing a head carriage assembly drive system for driving a head carriage assembly during a tracking/seek operation, the head carriage assembly drive system comprising:
a first drive unit for generating force to rotate a head carriage of the head carriage assembly, the first drive unit being provided, with respect to a pivot, on a side of the head carriage opposite a side on which a head is provided;
a second drive unit positioned at a position other than a position at which the first drive unit is positioned, the second drive unit having a torque constant or torque smaller than a torque constant or torque of the first drive unit; and
a control unit assigning mainly the first drive unit to operate in a low-frequency band and mainly the second drive unit to operate in a high-frequency band.
According to the head carriage assembly drive system described above, it is possible to greatly reduce power consumption compared to when only the second drive unit is used for tracking operation. The first drive unit operates only in the low-frequency band, so of the drive forces generated by the first drive unit the drive force of the primary resonance frequency that is the lateral mode caused by the bearing is small, and so the drive of the first drive unit does not cause the head carriage assembly to resonate. Additionally, the second drive unit has a small torque constant, with a primary resonance peak that is small. Control in the high-frequency bandwidth is performed by activating the second drive unit. Accordingly, tracking can be conducted with the same high degree of accuracy as when only the second drive unit is used.
Further, the above-described object of the present invention is also achieved by providing the head carriage assembly drive system comprising the first and second drive units as described above, wherein the control unit assigns the first drive unit to operate with respect to an eccentricity of the disk track and the second drive unit to operate with respect to other than an eccentricity of the disk track.
According to the head carriage assembly drive system described above, it is possible to greatly reduce power consumption compared to when only the second drive unit is used for tracking operation. The first drive unit operates only at the rotational frequency of the disk and therefore does not resonate at the frequency of the head carriage assembly (approximately 3-5 KHz). Additionally, the-second drive unit has a small torque constant, with a primary resonance peak that is small, and therefore is suitable for control through high-frequency bands. Accordingly, tracking can be conducted with the same high degree of accuracy as when only the second drive unit is used.
Additionally, the above-described object of the present invention is also achieved by providing a head carriage assembly drive system comprising the first and second drive units as described above, wherein the a control unit assigns the first drive unit to operate so as to supply a rotational force sufficient to offset a bias rotational force acting on the head carriage assembly, the second drive unit being driven to make the head follow the track on the disk.
According to the head carriage assembly drive system described above, power consumption can be greatly reduced compared to a case in which only the second drive unit is made to generate a rotational force to offset the rotational force caused by the cable while also being driven to make the head follow the track on the disk.
Further, the above-described object of the present invention is also achieved by providing a head carriage assembly drive system comprising the first and second drive units as described above, wherein the control unit assigns the first drive unit to detect a speed of movement of the head and assigns only the second drive unit to drive the head.
By using the first drive means to detect the speed of movement of the head, the need for a velocity estimator is eliminated, as is the need for the calculations performed by the estimator. Additionally, the speed of movement of the head is detected directly, making it possible to provide a more robust servo system. Moreover, calculation time is shortened and current flow begins quickly, providing accurate positioning and stable tracking.
Additionally, the above-described object of the present invention is also achieved by providing a head carriage assembly drive system comprising the first and second drive units as described above, wherein:
the second drive unit has a torque constant smaller than a torque constant of the first drive unit and generates a force that is the reverse of a force generated by the first drive unit, and the control unit; and
drive current sent to the first drive unit and drive current sent to the second drive unit, the values of the first and second drive unit currents being substantially inversely proportional to the torque constants of the first and second drive units.
According to the head carriage assembly drive system described above, the drive currents supplied to the first drive unit and the second drive unit are largely in inverse proportion to the torque constants of the drive units, and thus the force generated by the first drive unit and the force generated by the second drive unit are of equal size. As a result, the lateral forces acting on the pivot are cancelled out and only the torque of the periphery of the pivot acts on the head carriage. Accordingly, the lateral mode arising from the rigidity of the ball bearing is not excited and the servo bandwidth is increased, head slider positioning accuracy is increased and tracking accuracy improved.
Further, the above-described object of the present invention is also achieved by providing a head carriage assembly drive system for driving a head carriage assembly when making a head seek a target track on a disk during a seek operation, the head carriage assembly drive system comprising:
a first drive unit for generating force to rotate a head carriage of the head carriage assembly, the first drive unit being provided, with respect to a pivot, on a side of the head carriage opposite a side on which a head is provided;
a second drive unit having a torque constant smaller than a torque constant of the first drive unit; and
a control unit assigning the second drive unit to detect a speed of movement of the head and assigning only the first drive unit to drive the head.
According to the head carriage assembly drive system described above, using the second drive unit to detect the speed of movement of the head results in continuous speed information, eliminates the calculations by a digital signal processor (DSP) hitherto required in the conventional art, shortens the calculating time and thereby reduces the burden on the servo system by an equivalent amount. As a result, the seeking of a target track by the head is performed more stably and more smoothly than is the case with the conventional art.